A polyalkylene terephthalate, especially PET is manufactured and used in large quantities in the fields of living related materials such as fiber, film and resin, food related materials such as bottles for drinking water and carbonated drinks, and others because of its excellent chemical stability.
However, the disposal of wastes of fiber, film and resin products, and off-specification PETs, which are largely generated with increasing manufacturing quantities and consumption quantities, is presently becoming large social issues. Regarding material recycling, chemical recycling, thermal recycling etc., various methods have been proposed.
On the other hand, although especially the disposal of PET, bottles among the wastes is becoming more serious due to bulkiness, only material recycling that recovered used PET bottles are remelted and fibers are produced from the molten matter, is realized as a recycling method. But, when melt molding is simply used, it is not possible to reuse as PET bottles because of the deterioration of physical properties.
Further, a refilling method that PET bottles are washed and refilled has issues regarding the following, that is, who paying the cost of recovery, the points of safety and hygiene, and limitation in the number of times of reusing. The PET bottles are ultimately disposed, and the method can not be an permanent countermeasure. Further, PET bottle wastes contain foreign resins represented by polystyrene (hereafter, this may be abbreviated as PS), polypropylene (hereafter, this may be abbreviated as PP) and polyethylene (hereafter, this may be abbreviated as PE) which are originated from PET bottle product-constituting materials, for example, labels, shrink films, base caps, caps or the like, foreign plastics such as polyvinyl chloride (hereafter, this may be abbreviated as PVC) and polyolefinic resins, aluminum derived from caps and aluminum cans, iron derived from steel cans, adhesives, pigments, dyes and others.
Even in a bale of PET bottles recovered through collection of classified refuse, the mixing of foreign materials is hardly avoided. Even in chemical recycling that PET bottles are decomposed to monomers constituting the PET polymer by using a solvent such as water, methanol (hereafter, this may be abbreviated as MeOH) or ethylene glycol (hereafter, this may be abbreviated as EG), and the monomers are reused, the foreign materials generate various decomposition gases (for example, hydrogen chloride gas etc.) and various decomposition products (for example, lower hydrocarbons etc.) in the courses of heating process and reaction process, or mixed materials themselves sometimes largely deteriorate the quality of the monomer (DMT) recovered by chemical reactions, or they melt and become solid in recovering apparatuses to damage machinery and tools.
The chemical recycling includes, for example, a method by which polyester wastes are hydrolyzed in the presence of an alkali compound to obtain TA described in JP-A 11-21374 (JP-A means Japanese unexamined patent publication) and a method by which DMT and EG are obtained by gas phase MeOH decomposition in MeOH described in U.S. Pat. No. 5,952,520.
However, since these processes all need a reaction condition of high temperature of 200° C. or higher, they have very low allowance against the mixing of foreign plastics which start to decompose from the temperature of 190° C., for example, PVC and whose decomposed products cause quality deterioration of the final product.
Further, JP-A 2000-169623 describes a process in which PET wastes are decomposed with EG, the recovered bis-β-hydroxyethyl terephthalate (hereafter, this may be abbreviated as BHET) is purified by a thin-film evaporator, and subsequently the BHET is subjected to melt polycondensation to obtain PET polymer. However, this process also has a step imposing a heat history of 200° C. or higher, and the allowance of mixing of heat-decomposable foreign plastics such as PVC is small.
Namely, although chemical recycling has an allowance of the mixing of impurities larger than that of material recycling, it is required to remove the impurities almost completely in pretreatment processes. Further, it is generally known that the PET polymer for bottles is manufactured by obtaining an oligomer through an ester interchange reaction or an esterification reaction of DMT or TA used as a starting material with EG followed by a polycondensation reaction which is carried out successively. In this case, the DMT or TA of the raw material should be highly purified, and the contents of impurities should be sufficiently little; and otherwise, the obtained PET polymer can not be used for PET bottles.
Due to the circumstances having above mentioned various restrictions, no process capable of recovering effective components from used PET bottles through a chemical recycling process and again obtaining a PET polymer usable for PET bottles has been reported.